Title

Authors

Document Type

Article

Publication Date

Fall 1998

Abstract

Sulfolobus acidocaldarius had been found earlier to grow and desulfurize dibenzothiophene (DBT) in a tryptone medium. Its characteristics were investigated in a cheaper sucrose medium in this study. In DBT-free systems the growth at 70°C and pH 2.5 proceeded with a specific rate of 0.14 h−1 and a cell yield of 0.35 g dry cells g sucrose−1. The maximum cell concentration attainable in the fermentor (3.5 l) was only 0.4 g l−1 under the agitation speed of 600 rpm and aeration rate of 1 l min−1. It increased to 2.0 g l−1 with higher agitation (700 rpm) and aeration (2 l min−1). The strong dependency on agitation and aeration suggested that the growth limitation be related to the gas–liquid interfacial mass transfer, presumably for oxygen supply. As for the study of DBT desulfurization, immediate cessation of cell growth and rapid cell death were observed when an oil phase (2% in volume) containing 10 g l−1 DBT was added to the culture grown in the sucrose medium. Further experiments confirmed that DBT was responsible for the toxicity. Normal cell growth, however, could be obtained by employing gentle mixing to keep the oil and aqueous phases as rather separate layers. The water-soluble DBT was therefore not the cause of the toxicity and the contact frequency of the cells with the oil–water interface might play an important role. Under high agitation, the cells could also overcome the toxicity if a lower DBT concentration (2 g l−1) was involved. Nonetheless, no appreciable DBT transformation could be detected in any of the above systems. Sucrose was shown unsuitable as the substrate for the desulfurization process.